For more than a half century, conventional Si-based complementary metal-oxide-semiconductor (CMOS) transistors have been the mainstay of the electronic memory industry. Furthermore, Si-based flash memory's superior performance and its ease of fabrication compared to competing memory technologies has made it the dominant form of CMOS memory. However, the high standards of next-generation memory driven by rapidly growing demands have revealed the limits of current Si-based flash memory technology in terms of its fundamental scaling limitations, energy consumption, cost, and few microsecond switching speed. Although a wide variety of oxide-based materials and device structures for the replacement of the Si-based flash memories have been extensively investigated, none have adequately addressed future memory projections. Generally, the oxide-based resistive random access memories (RRAMs) can be categorized into unipolar, which can be programmed by the same voltage polarity, and bipolar memories, which can be programmed by reversing the voltage polarity. Many of the unipolar memories have demonstrated operation by nano-scale filamentary switching that allow them to follow an aggressive scaling trend; however, nano-scale metallic filaments can exhibit unstable switching behaviors, and high or unpredictable forming voltages (Vforming) due to the difficulty in controlling their stochastic formation. In contrast, bipolar memory has comparative advantages in the switching stability by an ionic movement or a redox process, with lower Vforming, and a broader range of materials availability. However, these come at the expense of lower switching ON-OFF ratios, limited thermal stability of the materials, or the limits of integration architectures to suppress sneak-currents in high-density crossbar arrays. Both unipolar and bipolar memory fabrications often involve high-temperature processes for materials depositions. Moreover, the devices commonly have a high switching current and need a compliance current (Ic) for preventing an electrical short, which requires an additional resistor on each cell and increases power consumption. To improve future nonvolatile memory, it is desirable to resolve the aforementioned challenges of each oxide-based memory system, such as by eliminating the need for I, or high temperature fabrication processes.
Nanoporous (NP) metal oxides have been widely used in electronics for energy production and storage. While NP materials have been used as templates for oxide memory applications, they have not yet been used as the active switching medium for resistive nonvolatile memory application.
The following disclosure discusses porous silicon oxide materials utilized as a unipolar switching medium and methods for fabricating porous silicon oxide materials. This new implementation of a porous oxide material in electronic devices meets the metrics desired for next-generation industrial performance. These new implementations also outperform present unipolar memory systems and can also bring advantages to bipolar memories. These can be used as memristors as well. Using this porous material structure, the stochastic formation of the switching filament may be controlled, which leads to significant improvements in device metrics, and the device can be fabricated at room temperature.